Electrical equipment, particularly medium-voltage or high-voltage electrical equipment, requires a high degree of electrical and thermal insulation between components thereof. Accordingly, it is well known to encapsulate components of electrical equipment, such as coils of a transformer, in a containment vessel and to fill the containment vessel with a fluid. The fluid facilitates dissipation of heat generated by the components and can be circulated through a heat exchanger to efficiently lower the operating temperature of the components. The fluid also serves as electrical insulation between components or to supplement other forms of insulation disposed around the components, such as cellulose paper or other insulating materials. Any fluid having the desired electrical and thermal properties can be used. Typically, electrical equipment is filled with an oil, such as castor oil, mineral oil, or vegetable oil, or a synthetic “oil”, such as chlorinated diphenyl, silicone, or sulfur hexafluoride.
Often, electrical equipment is used in a mission-critical environment in which failure can be very expensive, or even catastrophic, because of a loss of electric power to critical systems. In addition, failure of electrical equipment ordinarily results in a great deal of damage to the equipment itself and surrounding equipment thus requiring replacement of expensive equipment. Further, such failure can cause injury to personnel due to electric shock, fire, or explosion. Therefore, it is desirable to monitor the status of electrical equipment to predict potential failure of the equipment through detection of incipient faults and to take remedial action through repair, replacement, or adjustment of operating conditions of the equipment. However, the performance and behavior of fluid-filled electrical equipment inherently degrades over time. Faults and incipient faults should be distinguished from normal and acceptable degradation.
A known method of monitoring the status of fluid-filled electrical equipment is to monitor various parameters of the fluid. For example, the temperature of the fluid and the total combustible gas (TCG) in the fluid is known to be indicative of the operating state of fluid-filled electrical equipment. Therefore, monitoring these parameters of the fluid can provide an indication of any incipient faults in the equipment. For example, it has been found that carbon monoxide and carbon dioxide increase in concentration with thermal aging and degradation of cellulosic insulation in electrical equipment. Hydrogen and various hydrocarbons (and derivatives thereof such as acetylene and ethylene) increase in concentration due to hot spots caused by circulating currents and dielectric breakdown such as corona and arcing. Concentrations of oxygen and nitrogen indicate the quality of the gas pressurizing system employed in large equipment, such as transformers. Accordingly, “dissolved gas analysis” (DGA) has become a well-accepted method of discerning incipient faults in fluid-filled electric equipment.
In conventional DGA methods, an amount of fluid is removed from the containment vessel of the equipment through a drain valve. The removed fluid is then subjected to testing for dissolved gas in a lab or by equipment in the field. This method of testing is referred to herein as “offline” DGA. Since the gases are generated by various known faults, such as degradation of insulation material or other portions of electric components in the equipment, turn-to-turn shorts in coils, overloading, loose connections, or the like, various diagnostic theories have been developed for correlating the quantities of various gases in fluid with particular faults in electrical equipment in which the fluid is contained. However, since conventional methods of off-line DGA require removal of fluid from the electric equipment, these methods do not, 1) yield localized position information relating to any fault in the equipment, 2) account for spatial variations of gases in the equipment, and 3) provide real time data relating to faults. If analysis is conducted off site, results may not be obtained for several hours. Incipient faults may develop into failure of the equipment over such a period of time.
The measurement of hydrogen gas in the oil of an electrical transformer is of interest as it is an indication of the breakdown of the oil caused by overheating and/or arcing inside the transformer. Transformer oil cools the transformer and acts as a dielectric. As transformer oil ages it becomes a less effective dielectric. The increase in hydrogen dissolved in the transformer oil is an indicator of the coming failure of the transformer.
For large transformers there are hydrogen sensors that use gas chromatography or photo-acoustic spectroscopy to determine the amount of hydrogen gas within a transformer's oil. Such devices are very expensive and the expense is not justified for smaller transformers. There are many older, small transformers that could be monitored if a low-cost method of doing so was available.
A lower-cost gas monitor, the Hydran™ M2 manufactured by General Electric Company has been in use. However, this gas monitor only senses combustible gases and then uses a formula to estimate how much of the gas typically is hydrogen and how much is other gases.
An article “Overview of Online Oil Monitoring Technologies” by Tim Cargol at the Fourth Annual Weidmann-ACTI Technical Conference, San Antonio 2005 provides a discussion of oil gas measuring techniques, including hydrogen measurement.
Palladium hydrogen sensors are disclosed in Gases and Technology, July/August 2006, in the article, “Palladium Nanoparticle Hydrogen Sensor” pages 18-21. Palladium sensors are also disclosed in U.S. Patent Publications 2007/0125153-Visel et al., 2007/0068493-Pavlovsky, and 2004/0261500-Ng et al. U.S. Patent Application No. 2010/007828 discloses a hydrogen sensor for an electrical transformer.
There is a need for low-cost method of determining hydrogen gas content in oils, such as in electric power generation and transmission and distribution equipment especially transformers. There is a particular need for a method and apparatus for mounting a hydrogen sensor to electric power generation transmission and distribution equipment that does not require taking the equipment out of service and preferably uses existing fittings or ports in the equipment without the necessity of making new openings in the housings for the equipment. It would particularly advantageous to provide a method and apparatus for attaching a hydrogen sensor to a transformer or the like using the port used for a pressure sensor especially a rapid pressure rise sensor.